When Peter Jay turned 40 this past Feb. 7 it was for him "a real psycho-trauma."

"Like every man with a Peter Pan complex," he says, seeing himself age, I went into the darkest gloom, I worried about it for about three days. Then I came through it. I said to myself, "Okay, I'm middle aged, I'll adjust myself to the fruits of middle age."

But before he had a chance to tear off his legging and cap he was deemed once again, a youth.

Peter Jay was named British ambassador to Washington.

"Suddenly this happened," he says, "and all the world clamoured over my youth. It was a total reversal of self perception."

He smiles an ironic smile and takes a sip of his champagne cocktail and leans back on the linen sofa in the lounge of the Savoy Hotel. Peter Jay enjoys being interviewed.

He reaches over to light a small cigar, asks if it will offend.

"I'll smoke anything," he'll say with a shrug. "And I have no theories on smoking. I don't like to think about it. It scares me to death. It's more a fear of losing youth than it is a fear of death. On enjoys doing so many things."

By now everyone in Washington has heard about Peter Jay. And by the time he arrives in Washington late in July to relieve Sir Peter Ramsbotham, the current British ambassador, he will find an already mythical image to live up to.

In fact, not since the awaited arrival of John and Catherine Freeman two British ambassadors ago has Washington been so optimistically anticipating a new diplomat.

"Youthful," brilliant, handsome, clever, witty, charming, successful, gregarious, trendy Peter Jay; arrogant, vicious, overrated, insufferable, blatantly ambitious, pompous trendy Peter Jay.

He is still one of the most popular topics of conversation in London ever since it was announced he was to become ambassador. Manly because his close friend, 38-year-old Foreign Minister David Owen appointed him, never mind, of course, that his father-in-law just happened to be the prime minister.

"Nepotism," came the screams even from his closest friends. "How dare Callaghan appoint his daughter Margaret's husband."

"Inspired choice," countered his fans, particularly the editor of The Times of London where Jay had written an economics column for several years.

"Too young, too anti the British government," came back the detractors.

"Exactly," defended the Foreign Minister's office. "He'll get along beautifully with all those young Carter types, speak their language, be an iconoclast, anti-establishment like they are, fit right in, have great parties. He's trendy, they're perfect. The British embassy will be the focus of Washington social life."

Peter Jay winces.

"All ambassadors do a lot of entertaining but what I recoil from is this attempt to describe the job in these very pat cliche imagy terms. I, like everybody else, see myself as a human being with various weaknesses and vices like everybody else. I don't think in these Madison Avenue terms about what kind of imate and style I'll have."

"I'm sure that there will be a number of people who will be disappointed and think I am too conventional and there will also be a number of people who will think I'm not as conventional as I should be. But they will have to take me as I am, otherwise they'll just have to go to Central Casting for an ambassador. I recoil from putting myself in boxes. As trendy or whatever, I'm not a brand of soap.I don't intend to sell myself as that. The image thing is exactly the same thing as the age thing."

Peter Jay is very good looking in a sort of scruity English Oxford journalistic way. In fact, he has quite boyish looks. You can just picture him as a child in knickers playing soccer, with scrapes on his knees, his cheeks aflame from the chill of the English country air. He has a nice crinkly smile which seems most enthusiastic when he is expounding on some theory, arguing, making a point, analyzing, disputing, intellectualizing.

For Peter Jay is an intellectual. He is a wit. There is nothing he loves more than a challenging conversation.

If he is asked something controversial his whole face lights up with interest as he leans forward, expounds on whatever the subject is, then leans back satisfied and demands. "As me something else."

Those who know him well observe with a certain amusement that for Jay a challenging intellectual, thoughtful conversations is more like a sexual experience.

He is very sure of himself, there is no question about that, and it is not hard to see how he might be considered by some to be arrogant. Peter Jay sufers no fools gladly. But at this moment he is feeling his way along in a new situation, one that is the reversal of his former job as columnist and adversary of the government. Now he is part of the government and in that capacity he must reevaluate his quick tongue.

His outspokenness, he says is "something I'll have to deal with. I'll have to figure it out as I go along. I'm doing a different job but I'm still the same person."

Is that some person arrogant as well, as his critics say?

"I know I'm not arrogant in my mind and in my heart, I'd be a fool not to know I give the impression of being arrogant. I don't want to be arrogant. I don't feel arrogant. I can't feel arrogant. I don't approve of being arrogant."

He thinks the reason people say he's arrogant is that "I enjoy emormously the process of discussion. I have to worry about jumps in what I say or want to say, when I've got the point and the other person is still in the process of making a judgment. But that's exuberance, not arrogance. But I apologize to all those who think I'm arrogant."

He has been accused of writing esoteric copy, much too complicated for the average reader, as though he's communicating privately with the chancellor of the exchecquer and not to the masses.

"I think," he says, "that that's the opposite of arrogance. I think it's arrogant to write down." Oxford Scholar

He does have a slight sense of insecurity about his new role and that insecurity gives him an appealing air of vulnerability which, according to those who know him, is not characteristic.

In this respect he has much in common with the younger members of the Carter administration, those like Jody Powell and Hamilton Jordan who have been used to being on the outside, criticizing and are not themselves being criticized.

But that's about it. After spending over an hour with Peter Jay it would seem that Sir Peter Ramsbotham would be just as suited to them as Jay. For conversation is so important to him that he may find Washington's new crop somewhat of a dissapointment. They are, to be sure bright and quick and terrific with clever one-liners. But they would be the first to admit that they are hardly intellectuals and their idea of fun is much more likely to be an evening sitting in somebody's backyard, boozing and joking around, than it would be in a Georgetown salon ruminating for hours over theories and ideas. It's simply the difference between a Christ Church scholar at Oxford and a Pni Delta Theta fraternity man at the University of Georgia.

Peter Jay is uncomfortable with the diplomatic jargon which he will have to at least partially, assume.

He looks as though he is about to choke when he says, "I hope I am the best person for the job. My job will be to do the best I can. I am enthusiastic and dedicated to doing it." It just sounds as ambassadorial, so much the formula, pat, expected answer.

He grins a hit sheepishly. Caught well, he's got to practice on somebody. The Washington Scene

"Now," he'll say, changing the subject, "What is it they are saying about me?" He relishes this part of the interview, answering the attacks of his critics.

One of the things they say is that they can't understood why someone as supposedly brilliant as Peter Jay would want to be an ambassador, would want what some believe today is a non-job, an irrelevant position.

He pauses a moment to collect his thoughts.

"Well," he says, finally, taking another thoughful sip of his champagne cocktail and settling in on the sofa. "That is certainly a relevant question," he says. "Of course the role of ambassador today is clearly dfferent. Anybody who would try to pretend it wasn't would be crazy. In the days of the lone venturer," he says, "when it would take three months to reach each country by ship, there really was one issue and that was war and peace. Now with phones and the telex, the Concorde and so on, an awful lot will be conducted between the specialists of various governments.

"So anybody from my country who wants to go to Washington has got to get guidance on the Washington scene. Washington is a special and a complicated place. Knowing the place you're in is important for visiting firemen who come here: telling them how to go about things, telling them to whom they should make their pitch."

"And obviously," he says with a smile, "to make as many friends as you can for you country is certainly an objective."

Translated this means that basically, the job of ambassador is a public-relations job and for those with an interest in Washington social life it means that yes, the Jays will be doing a goodly amount of entaining. "Co-Ambassadress"

It has been said of Jay one reason he was appointed was because he was an economist and since Britain's major concern today is one of economics he will be largely their economist residence. He denies this.

"There are," he admits, "somethings to which economics is relevant. But I don't want to say, here I am, an economist. We have a lot of people in the embassy doing that. Of Course, it always helps to know about these things. One of the things people are interested in Britain is economics but I don't intend to go there as an economist or as an economic minister."

Everyone is curious about Jay's wife, Margaret Ann Callaghan, the 37-year-old daughter of the prime minister and a successful BBC-TV producer. There has been speculation that she will immediately begin looking for a job in TV when the Jays get to town, she being bright, aggressive and independent woman herself.

But no, Peter Jay sees his wife's role as being "co-ambassadress. She won't be doing any other work. She'll be full time with me. She's a very bright girl. A very modern girl. She's worked most of her life. That's normal and natural to her. In the last 11 years she's been a commuting reporter between the United States and Britain and she has spent quite long periods of time reporting in small places that people don't get to in the U.S. She spent over a month in Alliance, Ohio, during the last election, reporting the campaign there. As a result of all that she has a lot of knowledge about the U.S. and contracts from San Diego to Penobscot Bay.

"I think she can make a real contribution. There will be times when I can't go places."

"She can go in my place and give interviews, make speeches. I would hope she'd do it and be asked to do it on many subject and many topics.

"I'm sure this role of hers might be looked at as a contradiction for an ambassadress but I have friends I'm sure would agree that her role as ambassadress is an improvement on the role in terms of women's lib."

He seems unaware that there are those who think it is odd that a female television producer of great success and 11 years experience would give up her career for her husband's. He seems shocked when asked if she will continue her career.

"Not in a million years," he says with a near gasp. "This is going to be a full-time job for her. She's going to be flat out in this job. Besides, we have three small children ages 11, 9 and 5."

And when the Jays arrive late this July?"I shall pack them all off to Maine and got away if I can myself." "Nepotism" No Surprise

One of the things, one of the only things, everybody agrees on about Peter Jay is that he is a total Americanophile, a U.S.A. freak. He prides himself on being an expert on this country, knowing all the towns and cities, having mastered the slang understanding, digging, really, the American scene. The Jays were here for a year with The Times in 1969 before he returned to England and became the celebrated columnist and TV star. (He has a successful interview program in London.)

"Anybody is bound to be pleased by the job," says Jay. "Wouldn't you? I love the U.S."

The charges of nepotism, he says were something he "absolutely expected. It would have bothered me if I had thought there was some reason for it," he says. "I have a very high sensitivity to things that are wrong, improper or unfair. But it would be a hard day if the question had not been raised. Had I not known that it was the Foreign Secretary's plan rather than my father-in-law's I would have thought very carefully about it and I would have had grave, grave doubts. But I would never run away from the job because other people had doubts."

Naturally many of Jay's detractors don't believe a word of that. But their criticism doesn't worry him.

"Life," he says, "is too busy to worry about things like that. Basically I find life too fascinating, I find oneself extremely boring. To sit down and say, 'Why do I seem this way?' is paranoid and takes away from other, more worthwhile pursuits.

"Maybe there are things about me which deserves to be resented. Who knows? We'll leave it to anyone flattering enough to be interested. It's not a thing that hangs me up."

He likes that American expression and it rolls naturally off his tongue as though the patios were his own native tongue. "Natural Non-Worrier"

"I think," he says, "that I am one of the world's natural non-warriors. The time and energy one gives to one's actual problems is time enough without worrying as well about what people think of you."

For instance.

"Sometimes there are individual eases where I realise very few that I've offended somebody, given them a bad impression. And because I like the person or enjoyed the occasion I think, 'My God! I'm like that at all.' But I don't lie awake at night thinking what does the world think of me."

He has never been, nor will he ever go, to a psychiatrist.

"God No!" he will say with astonishment at the mere thought. "I think that is profoundly unhealthy. Wild horses woundn't drag me. The minute we surrender the ultimate responsibility for our sanity, that is the real slippery slop towards real emotional and mental failure. You've got to feel, in the last resort, that your sanity, your ability to deal with things, is your own reponsibilty, you own problem to ge that thing intact."

"Of most as a diplomatic afterthought, that's my opinion. I didn't mean to criticize anyone who does go to a psychiatrist, mind you." "Tribal Person"

"Now," he says, perching with relish on the edge of the sofa, ready to defend himself once more, "what else do they say about me?" He is told they say it is thought to be somewhat hypocritical that Jay, who has been a staunch critic of the British government, both in print and TV, is now planning to represent it.

He settles back in his chair. He grins. He knows how he'll answer this one. "That is a very fair question," he says.

"I've formulated a pretty somber idea of what's happening, not just in England or Europe but in all indsutrial nations. To warn people. Let's do some thing before it's too late.

"One of the reasons why Britain's reputation is not as high has been that over the decades British apologists and ministers have tended to tell a rosier story that has been borne out by subsequent events. The way to persuade people of the real story is to have credibility and the only way to do that is to tell the truth. I don't see any conflict with the problem or with the story I have to tell. Yes," he says, "I have a reputation for telling it as it is."

He is told that, grammar notwithstanding, the expression is "telling it like it is." He blushes and seems truly chagrined. "Alright," he says finally, not enjoying this at all, "I stand corrected."

Peter Jay is not, however, contrary to popular opinion, a totally cerebral human being. He is an athlete of sorts, and plays tennis, cricked, is "very keen" on sailing and plays bridge with relentless fascination. He is a classical music buff and loves to read but hardly ever reads fiction any more. "I read a lot of good bad books on airlines," he admits.

If Peter Jay had his wish of the perfect way to spend his time he would have no trouble deciding.

He fondles the stem of his champagne cocktail and looks a bit dreamily away as he conjures up the perfect vacation.

"I'd like to be at anchor in my boat at the Deer Island Thoroughfare listening to Motart's 41st symphony with a good cigar and a long voyage to start the next day," he says decisively. "That to me is pure poetry."

None!

"Oh no! Never, I'm not an alone person. I cannot bear to be alone. I detest being on my own. I'm a tribal person."

With that, he looks at his watch, jumps up and apologizes that he must run off to a dinner party. As he starts toward the door of the Savoy lobby he pauses, turns back and pleads with boyish charm, "I hope I haven't said anything disastrous. If I have, don't writ it. I'm all new. Please come and see us in that [WORD ILLEGIBLE] ." He half gags on the word, "Oh no," he moans "Don't print that."